The present invention relates to seismic land exploration and pertains particularly to seismic sensing units and methods of use thereof.
Seismic exploration is a technique commonly employed for exploring and mapping sub-surface formations. Such seismic exploration is used for many purposes such as the location of mineral bodies and reservoirs within sub-surface formations.
Such exploration is typically carried out by means of a system employing a plurality of sensing instruments coupled to the earth's surface which are utilized to detect sound waves travelling through and/or reflecting off of sub-surface formations. Such sound waves may be natural or manmade or may be generated in any number of ways.
The detectors used in such exploration are normally highly sensitive but normally have a single sensing axis. This sensing axis must normally be oriented vertically in order to accurately detect the sound waves which are also preferably travelling vertically. The coupling of the sensing instruments typically referred to as seismometers to the earth's surfaces is also very critical in order to insure that the signals are detected without undue damping.
These seismic exploration methods employ a plurality of the seismometers set out in arrays which may cover areas from a few hundred square yards to a few square miles. These arrays may also be set out in a straight line which may also vary in length anywhere from a few hundred yards to several miles.
Because of the need for vertical orientation of the seismometers as well as for adequate coupling thereof to the ground, a great deal of labor is normally involved in setting out and moving these arrays of seismometers. Many attempts at reducing or eliminating this labor has been proposed in the past. These proposals have involved either attempts to provide a geophone that does not require specific orientation or the provision of geophones which maintain their orientation and may be moved in strings such as towing without manual labor. Examples of the former approach are shown in the following U.S. patents:
U.S. Pat. No. 2,659,065 issued Nov. 10, 1953 to Cordell;
U.S. Pat. No. 2,792,562 issued May 14, 1957 to Baker;
U.S. Pat. No. 3,054,085 issued Sept. 11, 1962 to Alexander;
U.S. Pat. No. 3,810,083 issued May 7, 1974 to Kostelnicek.
An example of the latter is that disclosed in the following patents:
U.S. Pat. No. 3,689,875 issued Sept. 5, 1972 to Kostelnicek;
U.S. Pat. No. 3,825,886 issued July 23, 1974 to Thigpen.
While these proposals have achieved some limited degree of success, they still have some drawbacks.
Accordingly, it is desirable that a seismic sensing instrument be provided that is highly sensitive, self-erecting and easily coupled to the earth's surface.